The present invention relates to a decoupling element for pipelines subject to vibration. A typical example of an application would be in vehicle exhaust systems.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
Such devices are intended to connect in a flexible way pipes which are subject to vibration, and to protect them from vibration. In order to meet the requirements of the automotive industry (passenger cars) for gas-tightness, a metal bellows is often a module of such decoupling elements. As the large variations in diameter in the corrugations of the metal bellows may lead to turbulence, a metal hose is usually incorporated into the pipe so as to ensure laminar gas flow. It must be ensured that any noise generated during operation resulting from the metal hose hitting the inside of the bellows is kept to a minimum. This is often achieved by surrounding the hose with braiding. German Offenlegungsschrift DE 198 20 863 A 1 shows a flexible pipe as an example. Instead of using braiding, the metal hose and the metal bellows are connected at defined points so as to prevent the development of the type of noise described above.
For commercial vehicles, multi-layer wound metal hoses produced from profiled strip material are frequently used as decoupling element in exhaust systems. Since a low degree of leakage is permissible, it is not necessary to use a gas-tight element such as a metal bellows. A simple example of metal hoses used as decoupling elements is the so-called Agraff hose. Further examples, which have a longer service life and a lower leakage rate than Agraff hoses, have been described in German publications DE 34 41 064 C2 and DE 101 13 180 C2.
Wound metal hoses are especially suitable for the exhaust systems of commercial vehicles as they tolerate large offsets in the axial, lateral, and above all the torsional direction without structural tension arising. Their disadvantage, however, is the residual leakage.
As legal provisions worldwide will be stipulating a substantially reduced emission of pollutants from commercial vehicles, exhaust systems will increasingly be fitted with exhaust gas treatment modules such as soot filters and SCR systems. SCR systems in particular place new technical requirements on decoupling elements as they reduce nitrogen oxide in exhaust gas by adding AdBlue (=urea). AdBlue is injected into the exhaust gas flow. Depending on the service and ambient conditions, condensate may be formed on the inside walls of the exhaust system. Liquid urea has a good seepage ability and must not emerge from the exhaust system into the environment. For this reason, all pipes used in the exhaust system and in particular decoupling elements must be at least liquid-tight.
It would therefore be desirable and advantageous to provide an improved liquid-tight decoupling element to obviate prior art shortcomings and to prevent any penetration of condensate urea into the environment so as to be usable in exhaust systems in connection with SCR systems, while still allowing substantial movements in axial and in particular torsional direction.